Fluid extraction apparatus

ABSTRACT

A fluid extraction apparatus comprises a passage  20  for the pumped flow therealong of a first fluid, for example air. A fluid flow area control device in the form of an apertured plug  22  is present in the passage. An inlet  26  to the passage  20  is provided at or downstream of the downstream side of the plug  22.  When, in use, the first fluid is pumped along the passage through the aperture  23  of the plug  22  the fluid pressure at the inlet  26  is reduced causing a second fluid to be drawn into the passage  20  via the inlet  26  to flow with the first fluid towards the downstream end of the passage  20.  The downstream end of the passage may be provided with a filter  6  in the form of a tank  8  containing an oil dissolving agent  10.  The apparatus has a particular application to a cooker hood assembly for extracting a gas from a cooker hood  2,  without having to pass the gas through a pump  4,  and then treating the extracted gas to remove pollutants such as water, oil droplets and smoke therefrom.

The present invention relates to fluid extraction apparatus,particularly, but not exclusively, to apparatus for use in thepacification, purification or expulsion of a fluid, for example drawinga gas or liquid from a first area and transporting it to a second areaat which it may optionally be treated. The present invention hasparticular application, but is not restricted, to use in the extractionand filtering of air containing impurities such as smoke, water vapouror oil vapour. Such an apparatus can be particularly useful in a cookingenvironment and could be employed in connection with a cooker hood abovea cooking apparatus.

Normal extractor fans or cooker hoods generally use some form of fan inthe path of the air to be extracted. Even if the fan is positioneddownstream of a filter, oily impurities in the air can become depositedon the fan.

According to the present invention there is provided fluid extractionapparatus comprising:

a passage having an upstream end, a downstream end and a cross-sectionalflow area for the pumped flow therealong of a first fluid in adownstream direction;

a fluid flow area control device having an upstream side and adownstream side and providing at said downstream side an increase in theavailable cross-sectional flow area of said passage between saidupstream and downstream ends; and

an inlet to said passage at or downstream of said downstream side ofsaid device;

whereby pumped flow of the first fluid along said passage past saiddevice reduces the fluid pressure at said inlet to cause a second fluidto be drawn into said passage via said inlet to flow with the firstfluid towards said downstream end.

Said fluid flow area control device advantageously provides an abruptincrease in the available cross-sectional first fluid flow area of saidpassage at its downstream side.

In a preferred arrangement the passage downstream of the fluid flow areacontrol device is contained within a first conduit and a second conduit,for the supply of the second fluid to the inlet, branches into the firstconduit at a branch junction.

The fluid flow area control device may take the form of a plug situatedin the first conduit, with the passage passing though at least oneaperture provided in the plug. The device may further comprise a hollowextension pipe extending downstream from the downstream side of theplug, beyond the branch junction, with the passage passing through theplug's aperture and through the pipe.

In an alternative arrangement a downstream portion of the second conduitextends into the first conduit, beyond the branch junction, and extendsin the downstream direction. The exterior surface of the downstreamportion of the second conduit can be spaced from the surroundinginterior surface of the first conduit to form therebetween an annularspace through which the passage passes. In this way the downstreamportion of the second conduit forms the fluid flow area control device.

The present invention will now be described, by way of example only,with reference to the accompanying drawings, in which:

FIG. 1 is a schematic sectional side view of apparatus according to afirst embodiment of the present invention;

FIG. 2 is a cross-section along the line II—II in FIG. 1;

FIG. 3 is a schematic sectional side view of apparatus according to asecond embodiment of the invention;

FIG. 4 is a schematic sectional side view of apparatus according to athird embodiment of the present invention;

FIG. 5 is a cross-section along line V—V in FIG. 4;

FIG. 6 is a schematic sectional side view of apparatus according to afourth embodiment of the invention; and

FIG. 7 is a cross-sectional view along the line VII—VII in FIG. 6.

A schematic sectional side view of the first embodiment of apparatus inaccordance with the present invention is shown in FIG. 1. The embodimentis sectioned along the longitudinal axis of a first passage 20 and asecond passage 24. For clarity, the thin wall materials of the conduitsforming these passages, as well as other elements of the apparatus, havebeen shown schematically as having no thickness.

This embodiment consists of a cooker hood 2, an air compressor 4, afiltering section 6, a control valve 12, a first passage 20, a fluidflow area control device 22 and a second passage 24 connected at adownstream portion of the first passage (i.e. a down stream passage).

In operation of this first embodiment the compressor 4, which may be afan, pumps a first fluid (in this example, air) into the upstream, lefthand end of the first passage 20. The amount of air passing through thefirst passage 20 is controllable by a control valve 12. Downstream ofthe valve 12 the pumped air passes through a fluid flow area controldevice 22, past a branch junction 26 where the second passage 24branches into the first passage 20 and along the downstream portion 28of the first passage before passing into the filter section 6 at thedownstream end of the first passage 20.

The fluid flow area control device 22 in the first embodiment is acylindrical plug with a small cylindrical aperture 23 provided along itscentral axis, coaxial with the longitudinal axis of the first passage20, as shown in FIG. 2. As the pumped air enters into the opening of theaperture 23 in the upstream side of the plug 22 the air will acceleratedue to the decrease in the available cross-sectional flow area of theaperture 23, relative to the cross-section of the first passage 20upstream of the upstream side of the plug. Upon exiting the aperture 23at the downstream side of the plug 22 and passing into the widercross-sectional flow area of the first passage 20 in the region of thebranch junction 26 adjacent the inlet formed by the second passage 24,the high velocity of the pumped first fluid (air) creates a low pressureregion in the vicinity of the inlet of the second passage 24. In theillustrated embodiment the air pressure at the cooker hood will beapproximately atmospheric pressure. The low pressure region thus draws asecond fluid (in this example, cooking fumes largely comprising air)through the second passage 24 from the cooker hood 2. This drawn airthen flows with the pumped air along the remainder of the first passage20 to the filter section 6.

If the air in the cooker hood contains impurities such as smoke, air,steam or oil droplets, then these can be readily removed at the filtersection 6. In this embodiment the filter section 6 has a tank 8containing oil dissolving agents 10 into which the mixture of pumped anddrawn air passes. In this way any oil droplets in the second fluid (air)can be removed. Other chemical or physical filters may be used insteadof this tank or in addition to it. For instance, activated charcoalcould be used to remove smoke and/or a desiccant could be used to removewater vapour. These other filters could be provided within thedownstream portion 28 of the first passage or after the oil filter. Thefilters could be arranged in any effective order or in any suitablecombination. The filters present could be matched to whatever impuritiesit is desired to remove from the incoming fluid.

The filter section is optional. If, for example, the mixture of pumpedand drawn air was to be vented from downstream portion 28 direct toatmosphere, the filter section could be omitted.

By the time the air has passed through the filter section 6 it can bereturned to the closed environment from which it came, for example akitchen, or simply be expelled to atmosphere containing fewer impuritiesthan if it had not been filtered.

In the illustrated embodiment of filter section 6, the end of theconduit forming the first passage 20 is surrounded by an outer pipe 14of a greater diameter than the conduit. Holes 18 are provided in theperimeter of the lower end of this outer pipe which is in the tank andthe air mixture passes through these into the oil dissolving agents.This arrangement reduces bubbling in the tank 8.

The small, central through-aperture 23 used in the fluid flow controlelement 22 has been found to be more effective than a simple gap betweentwo halves of a fixed plug. The suction force generated at thedownstream side of the flow control element 22 at branch junction 26 isgreater for the same air pressure produced by the pump 4.

The diameter of the through-aperture 23 can be reduced to increase thesuction at the inlet of the second passage 24. For a fixed first fluidflow rate, the smaller the size of the aperture 23, the greater will bethe velocity of the first fluid when it exits the downstream side of thefluid flow area control device 22. In this illustrated embodiment thediameter of the aperture 23 is between 1 mm and 3 mm.

The entire portion of the first passage between the pump and thedownstream side of the fluid flow area control device 22 can be providedwith a constant cross-section that is reduced relative to the availableflow cross-section downstream of said downstream side, so that the fluidflow area control device 22 simply acts to define an abrupt increase inthe available cross-sectional flow area available to the first, pumpedfluid at the downstream side of the device 22. However, this can lead toexcessive resistance to the flow of the first fluid. Consequently, as inthe illustrated embodiment, it is preferred for the fluid flow areacontrol device 22 to be of restricted axial length, for example betweenabout 20 mm and 100 mm. In this way the device 22 defines a reduction inthe available cross-sectional flow area upstream of its upstream side aswell as defining an abrupt increase in the flow area downstream of itsdownstream side.

In this illustrated embodiment the passage 20,24 are defined by conduitsin the form of round pipes of between approximately 13-25 mm indiameter. The internal diameter of the conduit forming the first passage20 matches the external diameter of the cylindrical plug 22.

The control valve 12 is preferably, as shown, present in the conduitforming the first passage 20 after the air compressor 4 but before theupstream side of the fluid flow control element 22. The valve 12 can beused to control the air pressure in the apparatus, for example if thebubbling action in the tank 18 becomes too great the air pressure mayneed to be reduced. Alternatively, the valve 12 can be useful if thesuction of the second fluid (air) is too great and the air causes toomuch noise. The use of the control valve 12 may be in addition to, or asan alternative to, controlling the power supplied to the air compressor4.

The length of the conduit forming the second passage 24 between the hood2 and the first passage 20 can be chosen to suit individual usage. Formost effective results this conduit is typically no more than 2000 mmlong; beyond that the effectiveness of the apparatus reduces.

In the first illustrated embodiment the conduit forming the secondpassage 24 meets the conduit forming the first passage 20 atapproximately right angles to form a branch junction. This centre of thebranch junction may advantageously be positioned between about 0 mm and100 mm downstream of the downstream side of the fluid flow area controldevice 22. In this way the main high velocity flow of pumped first fluid(air) flowing through the aperture 23 in the plug 22 does not dispersesufficiently to fill the whole of the expanded cross-sectional area ofthe first passage 20 by the time that the inlet of the second passage 24is reached at the branch junction.

In FIG. 1 the downstream side of the plug 22 is shown as being spacedfrom the branch junction 26. The inlet for the second fluid, at whichthe first and second fluids are exposed to each other for the firsttime, is coincident with the branch junction 26 in this firstembodiment. Consequently, the inlet is also spaced downstream of thedownstream side of the plug 22.

A second embodiment of apparatus in accordance with the presentinvention is shown in FIG. 3. This embodiment is similar to that shownin FIG. 1, except for the provision of an extension pipe 30. In thissecond embodiment the effectiveness of the apparatus is increased, i.e.the suction generated in the second passage 24 is increased withoutrequiring a corresponding increase in the air pressure supplied by thecompressor 4. The extension pipe 30 has an internal diameter similar tothat of the aperture 23 in the plug 22 and is connected directly to thedownstream end face of the plug 22 with its opening aligned with theplug aperture 23. It has been found that good results are achieved whenthe length of the extension pipe 30 is about 200 mm, with the branchjunction between the first and second passages 20, 24 beingapproximately midway along the axial length of the pipe 30, as shown inFIG. 3.

In this second embodiment the fluid flow area control device comprisesboth the apertured plug 22 and the extension pipe 30. The downstreamside of the device, formed by the extreme right hand end of the pipe 30,is positioned downstream of the branch junction 26. In addition, theannular inlet 60 for the second fluid, at which the first and secondfluids are exposed to each other for the first time, is also positioneddownstream of the branch junction 26.

A third embodiment of apparatus is illustrated in FIGS. 4 and 5. Theprinciple of operation of this third embodiment is similar to that ofthe previous embodiments. Where the same components exit in the thirdembodiment they have been given the same reference numbers as in theprevious embodiments.

The difference between the third and first embodiments is in the form ofthe fluid flow control device 70. In the third embodiment this devicecomprises a solid, cylindrical plug positioned coaxially in the conduitforming the first passage 20. The diameter of the plug 70 is such thatthe plug's exterior surface is spaced from the surrounding cylindricalinterior surface of the conduit to form therebetween a generally annularspace through which the passage passes. In FIG. 5 the plug 70 is shownas being supported in the conduit by three radially extending supports72. Other forms of support may be used. As with the first embodiment theplug 70 is of restricted axial length, for example between about 20 mmand 100 mm.

In FIG. 4 the downstream side of the plug 70 is shown as being spacedfrom the branch junction 26. The inlet for the second fluid, at whichthe first and second fluids are exposed to each other for the firsttime, is coincident with this branch junction 26. Consequently, in thethird embodiment the inlet is also spaced downstream of the downstreamside of the plug 70. The downstream side of the plug 70 may need not,however, be spaced from the branch junction 26 (not shown).

In the fourth embodiment illustrated in FIGS. 6 and 7, a similar systemis used to that shown in FIGS. 1 and 2. Where the same components existin the fourth embodiment they have been given the same reference numbersas those in the first embodiment.

In the fourth embodiment the differences are in the form of the fluidflow area control device and the inlet of the second passage 42. As canbe seen in FIG. 4, the downstream end of a second passage 42 is formedby a second conduit 52 that meets and passes at an angle into a firstconduit 62 forming the first passage 40 and continues coaxially withinthat first conduit 62. Thus the pumped air flowing within the firstpassage 40 must flow through a reduced cross-section annular passage 50formed between the outside of the downstream portion of the secondconduit 52 and the inside of the first conduit 62 as far as the end ofthe second conduit 52. At the extreme downstream end of the secondconduit 52 the cross-sectional flow area available to the pumped firstfluid increases abruptly.

In this fourth embodiment the downstream portion of the second conduit52 acts as the fluid flow area control device, so that the availableflow cross-section for the pumped fluid increases abruptly on exitingfrom the reduced cross-section annular passage 50. As in the previousembodiments, this increase in the flow cross-section available to thepumped fluid creates a region of reduced pressure at the downstream endof the fluid flow area control device, causing air from the cooker hood2 to be drawn up along the second passage 42 into the first passage tothen pass downstream with the pumped air, as in the earlier embodiments.

In this fourth embodiment the annular passage 50 around the extremedownstream (right hand) tip of the second conduit 52 forms the inlet forthe second fluid, at which point the second fluid is exposed to thepumped, first fluid for the first time.

To give good efficiency, the annular passage 50 between the co-axialportion 44 of the second conduit 52 and the coaxial portion of thesurrounding conduit 62 forming the first passage 40 is quite small andof constant cross-sectional area. Setting this radial gap “h” (see FIG.7) to be between about 0.5 and 1.0 mm and making this co-axial regionbetween about 20 mm and 100 mm long has been found to give particularlyeffective results. Excessive increases in the length of the reducedcross-section annular passage 50 reduce the overall efficiency of theapparatus.

The conduit 52 forming the second passage 42 branches into the conduitforming the first passage 40 in the fourth embodiment at an angle. Thishelps to improve the efficiency over the two conduits branching togetherperpendicularly. However, a perpendicular branch is possible.

The described and illustrated embodiments can be used with a variety ofconduit or pipe sizes and shapes. The apparatus may be scaled up or downin size. Furthermore, the length of the different conduit portions canbe changed. For example, the length of the conduit forming the secondpassage 24, or the length of the main part of the conduit forming thefirst passage 20 after the first and second conduits branch into oneanother can be varied. The diameter of the first conduit can, forexample, be increased above the preferred 13-25 mm range mentionedearlier. The capacity of the air compressor 4 may need changing tomatch.

Although the conduits shown are pipes having circular cross-sections,conduits with other cross-sections are usable. Equally, the conduits donot need to be of constant cross-section or generally straight.

The illustrated and described embodiments are examples of the presentinvention being used with air as the pumped fluid and the drawn fluid.The apparatus is, however, operable with other gases or with liquids,for example water. When the apparatus is operated with water instead ofair, the air compressor 4 can be replaced by a corresponding device,such as, for example, a water pump.

What is claimed is:
 1. A fluid extraction apparatus comprising: a firstpassage; a fluid providing mechanism connected to an upstream side ofthe first passage and providing a first fluid to the first passage; afluid flow area control device provided along the first passage andreducing a cross-sectional area of the first passage through which thefirst fluid passes; a downstream passage connected to the first passagedownstream of the fluid flow area control device; a second passageconnected to the downstream passage downstream of the fluid flow areacontrol device, the second passage being distinct from the first passageupstream of the fluid flow area control device; whereby the pressure ofthe first fluid at a downstream side of the fluid flow area controldevice is reduced to bring a second fluid from the second passage intothe downstream passage, the second fluid being separate from the firstfluid in the first passage before the first fluid and the second fluidmeet in the downstream passage.
 2. The fluid extraction apparatusaccording to claim 1, wherein the at least one aperture comprises asingle central aperture coaxially aligned with a longitudinal axis ofthe first conduit.
 3. The fluid extraction apparatus according to claim2, wherein a cross-sectional area of the aperture perpendicular to thelongitudinal axis is substantially constant.
 4. The fluid extractionapparatus according to claim 1, further comprising a filter section thatis positioned at a downstream end of the downstream passage and purifiesan incoming fluid from the downstream passage.
 5. The fluid extractionapparatus according to claim 4, wherein the filter section comprises atank containing oil dissolving agent in which the downstream passage isimmersed so that the incoming fluid from the downstream passage passesthrough the oil dissolving agent.
 6. The fluid extraction apparatusaccording to claim 4, further comprising a cooker hood connected to thesecond passage.
 7. The fluid extraction apparatus according to claim 1,further comprising a control valve that is provided in the first passageand regulates an amount of the first fluid.
 8. The fluid extractionapparatus according to claim 1, further comprising an extension pipeextending from the downstream end of the single central aperture in theplug to a downstream side of a junction connecting the second passagewith the downstream passage.
 9. The fluid extraction apparatus accordingto claim 8, wherein the junction is substantially at a center of alength of the extension pipe.
 10. The fluid extraction apparatusaccording to claim 9, wherein the length of the extension pipe isbetween about two to about ten times of an axial length of the plug. 11.The fluid extraction apparatus according to claim 3, wherein when adiameter of the aperture is between x and 3x, the axial length of theplug is in the range of between 20x and 100x.
 12. The fluid extractionapparatus according to claim 1, wherein the fluid flow area controldevice comprises a plug positioned so that a gap is provided between anexterior surface of the plug and an interior surface of the firstconduit, the first fluid passing through the gap from the first passageto the downstream passage.
 13. The fluid extraction apparatus accordingto claim 11, wherein the plug is coaxially aligned with a longitudinalaxis of the first conduit.
 14. The fluid extraction apparatus accordingto claim 1, wherein the second passage is connected to the downstreampassage at substantially a right angle.
 15. The fluid extractionapparatus according to claim 1, wherein the fluid flow area controldevice is arranged to provide an abrupt increase in the cross-sectionalarea of the first passage at the downstream side of the fluid flow areacontrol device.
 16. The fluid extraction apparatus according to claim 1,wherein the fluid providing mechanism is an air compressor.
 17. A fluidextraction apparatus comprising: a first conduit; a fluid providingmechanism connected to an upstream side of the first conduit andproviding a first fluid to the first conduit; a second conduit that isinserted into the first conduit at an intermediate portion of the firstconduit, an inserted portion of the second conduit being directed to adownstream side of the first conduit and being aligned with the firstconduit so that a gap is provided between an exterior surface of thesecond conduit and an inner surface of the first conduit, the firstfluid passing through the gap; whereby a pressure of the first fluid atan end position of the second conduit in the first conduit is reduced tobring a second fluid from the second conduit into the first conduit, thesecond fluid being separate from the first fluid in the first conduit.18. The fluid extraction apparatus according to claim 17, wherein alength of the inserted portion of the second conduit aligned with thefirst conduit is between 20 mm and 100 mm, and a width of the gap isbetween 0.5 mm and 1 mm.
 19. The fluid extraction apparatus according toclaim 17, wherein the inserted portion of the second conduit alignedwith the first conduit is coaxial to the first conduit.
 20. The fluidextraction apparatus according to claim 17, further comprising a filtersection that is positioned at a downstream end of the first conduit andpurifies a fluid from the first and second conduits.
 21. The fluidextraction apparatus according to claim 20, wherein the filter sectioncomprises a tank containing an oil dissolving agent in which the firstconduit is immersed so that the fluid from the first and second conduitspasses through the oil dissolving agent.
 22. The fluid extractionapparatus according to claim 20, further comprising a cooker hoodconnected to the second conduit.
 23. The fluid extraction apparatusaccording to claim 20, further comprising a control valve that isprovided in the first passage upstream of a junction of the first andsecond conduits, wherein the control valve regulates an amount of thefirst fluid.
 24. The fluid extraction apparatus according to claim 17,wherein the fluid providing mechanism is an air compressor.
 25. Thefluid extraction apparatus according to claim 1, wherein the fluidproviding mechanism is a water pump.
 26. The fluid extraction apparatusaccording to claim 17, wherein the fluid providing mechanism is a waterpump.
 27. A fluid extraction apparatus comprising: a first passage; afluid providing mechanism connected to an upstream side of the firstpassage and providing a first fluid to the first passage; a fluid flowarea control device provided along the first passage and reducing across-sectional area of the first passage through which the first fluidpasses; a downstream passage connected to the first passage downstreamof the fluid flow area control device; a second passage connected to thedownstream passage downstream of the fluid flow area control device, thesecond passage being distinct from the first passage upstream of thefluid flow area control device; whereby the pressure of the first fluidat a downstream side of the fluid flow area control device is reduced tobring a second fluid from the second passage into the downstreampassage, the second fluid being separate from the first fluid in thefirst passage before the first fluid and the second fluid meet in thedownstream passage, wherein the cross section of the first conduit issubstantially constant, wherein the second conduit extends outwardlyfrom the peripheral surface of the first conduit, and wherein all of thefluid in the first conduit passes through the fluid flow control device.